Fingerprint image generating method and fingerprint image recording sheet

ABSTRACT

A fingerprint image generating method and a fingerprint image recording sheet are provided which can take a clear fingerprint image easily and efficiently, without the process of wiping seal ink, with less chance to generate an unclear fingerprint image even in improper operation. A solution containing an electron-donating dye precursor is applied to a fingerprint face of a fingertip and then the fingertip is pressed against a recording film to which an electron-accepting color developer is applied. The electron-accepting color developer adsorbs the electron-accepting dye precursor to occur a coloring reaction on the recording film. The fingerprint image recording sheet includes a fingerprint image recording portion applying the electron-accepting color developer thereto and the electron-donating dye precursor applied portion to which the solution of the electron-donating dye precursor is applied. The solution containing the electron-donating dye precursor is preferably microencapsulated and applied to the support. It is preferable to form the microcapsules to be ruptured merely by rubbing it lightly with the fingertip.

This is a Divisional of application Ser. No. 08/641,651 filed May 1,1996, pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a fingerprint image generating method in whicha rising streamline patterned image on a fingerprint face of a fingertipis generated with a transferring technique and to a fingerprint imagerecording sheet practically which may be employed for the fingerprintimage generating method.

2. Related Art

Fingerprints have been used as means for identifying a person, forexample, in a field of the judicial office for identifying a suspect ofa violation of traffic regulations or a criminal.

Conventionally, such fingerprints (fingerprint images) have been takenin the following manner that the fingerprint face of the fingertip ispressed against black seal ink so that the seal ink can adhere to thefingerprint face, and then pressed against a recording sheet. In otherwords, the seal ink adheres to a projecting portion (also referred as toa rising streamline) on the fingerprint face which has an uneven patternso that the pattern of the projecting portion (rising streamline) can betransferred to the recording sheet, thus obtaining the rising streamlinepatterned image of the fingerprint.

In such a conventional method, the black seal ink remained on thefingertip after taking of fingerprint image needs wiping with a tissuepaper or a cloth, but it is too difficult to wipe off because the sealink filled in hollow portions of the uneven pattern on the fingerprintface can not be easily wiped away. Further, the tissue or the clothneeds preparing for wiping the seal ink and disposing thereof after endoperation of wiping, resulting in an increase of incidental work.

On the other hand, the recording sheet to which the seal ink istransferred can not be piled up with other documents until thetransferred ink dries or unless the wet and excess ink is removed bypressing with a blotter. For this reason, another problem arises thatworkability is lowered due to time needed for drying the seal ink aftertaking the fingerprint. Further, in this method, the image of the risingstreamline becomes so bold as to lose the pattern thereof when the sealink is used to excess for application to the fingerprint face, so that aclear fingerprint image can not be obtained.

Furthermore, when performing improper operation such as to press thefingerprint face excessively against the recording sheet or to slightlymove the fingertip while pressing it against the recording sheet, theclear rising streamline patterned image of the fingerprint can not beclearly obtained as well. Thus, it is impossible to make a judgment onfinely distinct fingerprint patterns not only in visual inspection, butalso in a computing process after reading the fingerprint with afingerprint reader.

SUMMARY OF THE INVENTION

The present invention has been accomplished under the circumstances asaforementioned, and an object thereof is to provide a method to generateor record a fingerprint image, which can save the trouble of doing aftertaking the fingerprint such as to wipe seal ink, so that a clearfingerprint image can be obtained easily and efficiently with lesschance to generate an unclear fingerprint image even in improperoperation.

Another object of the present invention is to provide a recording sheetwhich may be employed for one embodiment of the above method.

The former object of the present invention is attained by the provisionof a method of generating a fingerprint image comprising steps ofapplying solution to a fingerprint face of a fingertip, the solutioncontaining an electron-donating dye precursor dissolved therein; andpressing the fingertip against a recording film to which anelectron-accepting color developer is applied so that theelectron-donating dye precursor is adsorbed by the electron-acceptingcolor developer to occur a coloring reaction therebetween on therecording film.

In the present invention, it is preferable to apply micro-encapsulatedsolution to a support so that the solution is applied to the fingerprintface by rubbing the solution-applied surface on the support with thefingerprint face of the fingertip. In this case, the microcapsules canbe preferably ruptured upon application of pressure of approximately 0.2to 0.6 MPa, that is, can be ruptured merely by rubbing the solutionapplied surface lightly with the fingertip.

Then, the amount of oil to adhere to the fingertip is set mostpreferably so that the amount of the solution to be transferred to therecording film by pressing the fingertip against the recording filmfalls in a range of 20 to 100 μg/cm².

The latter object of the present invention is attained by the provisionof a fingerprint image recording sheet comprising:

a fingerprint image recording portion to which an electron-acceptingcolor developer is applied; and

an electron-donating dye precursor applied portion to which a solutionof an electron-donating dye precursor is applied, the electron-acceptingcolor developer being capable to adsorb the electron-donating dyeprecursor to occur a coloring reaction on the fingerprint imagerecording portion.

It will be understood that the electron-donating dye precursor may bemicroencapsulated and applied. The fingerprint-image recording portionand the electron-donating dye precursor applied portion can be formed indifferent regions adjacent to each other. Further, the above twoportions may be provided in different positions on the recording sheetsuch as forth and back faces, or in different pages. In these cases, ifthe fingerprint-image recording portion is covered with alight-shielding film capable of opening and closing, aged changes orcolor fading on the recording portion can be prevented.

Furthermore, the electron-donating dye precursor applied portion may beformed on the film covering the fingerprint image recording portion. Inthis arrangement, the covering film is opened or removed when taking afingerprint so that the fingerprint face can be pressed against the thusbared recording portion usually covered with the film. After that, therecording portion is closed or covered with the film again. The coveringfilm may be a light-shielding type the upper face of which is coatedwith the electron-donating dye precursor.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages and further description will nowbe discussed in connection with the drawings in which:

FIG.1 is a descriptive diagram showing a general idea of a methodaccording to the present invention;

FIG. 2 is a flow chart showing processing steps of the method;

FIGS. 3A-3D are diagrams showing comparison between enlarged fingerprintimages respectively formed according to the present method and aconventional method; and

FIGS. 4A, 4B and 4C are diagrams showing embodiments to which thepresent invention is applied.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a reference numeral 10 denotes an electron-donating dyeprecursor applied film (hereinafter, also referred as to a color-formerapplied film), which comprises a support sheet 12 and a microcapsulelayer 14. The microcapsule layer 14 is formed on an upper face of thesupport 12 with an electron-donating dye precursor (hereinafter, alsoreferred as to a color former) in a microcapsulated condition. Thesupport 12 may be made of a plastic film, a metal foil, a resin coatedpaper or a synthetic paper. The microcapsule layer 14 is formed byapplying a microencapsulated solution of the color former in an oil.

The color former is a colorless compound which develops some color uponcontact with an electron-accepting color developer (hereinafter, alsoreferred as to a color developer). The color developer is a solid acid,more specifically an electron-accepting solid acid. The color formersand color developers are well known in the art. More detaileddescription of microcapsules, color formers and color developers whichmay be used in this invention will be found, for example, in JapanesePatent Publication Nos. 57-24852 (corresponding U.S. Pat. No. 4,002,060)and 59-16654 (corresponding U.S. Pat. No. 4,132,112). The descriptionsin the specification of these prior patents will be incorporated hereinas the references.

The color former is dissolved in an oil. The oil used herein is alsodisclosed in the above documents, for example, synthetic oil or naturaloil can be used. The solution of the color former is microencapsulatedwith a known microencapsulation technique, for example, disclosed inU.S. Patent Nos. 4,002,060 and 4,132,112. As such techniques,coacervation, surface polymerization, internal polymerization andexternal polymerization are cited.

The microencapsulated color former solution (microcapsule containedsolution) is a capsule dispersed solution, so that it can be applied tothe support 12 as it is for forming the microcapsule layer 14. It isnoted hereby that the microcapsules are regulated to have a strength orresistance as to be easily ruptured when rubbed with a fingertip,preferably to be able to be ruptured upon application of pressure ofapproximately 0.2 to 0.6 MPa (MPa: mega-pascal, 1 MPa≈10.2 kgf/cm²).

In FIG. 1, a reference numeral 16 denotes a recording film constitutedof a support 18 and a layer containing an electron-accepting colordeveloper (hereinbelow, simply referred as to a color developer) 20. Thesupport 18 used herein may be the same as the support 12 used in thecolor-former applied film 10. The color developer may be either aninorganic solid acid or an organic compound. Such color developers aredisclosed in the aforementioned prior art documents. As the color-formerapplied film 10 and the recording film 16, a pressure measuring system"PRESCALE" (trade name) for ultra-super-low pressure, commerciallyavailable from FUJI PHOTO FILM CO., LTD. can be used.

The color-former applied film 10 and the recording film 16 mentionedabove are prepared and used for taking a fingerprint image through thefollowing processing steps. First, a fingerprint face 24 of a fingertip22 (FIG. 1) is put into contact with the microcapsule layer 14 on thecolor-former applied film 10 so that the microcapsule layer 14 is rubbedtherewith (step 100 in FIG. 2). Consequently, the microcapsules in themicrocapsule layer 14 are ruptured so that the solution of the colorformer sealed in the microcapsules adheres to the fingerprint face 24.The fingertip 22 to which the color former solution adheres is thenpressed against the color-developer layer 20 on the recording film 16(step 102), so that the solution of the color former adhering to thefingertip is transferred to the color-developer layer 20, and so thatthe color former contained in the ruptured capsules is adsorbed togetherwith the oil solution by the color developer to develop a color, red inthe illustrated embodiment (step 104).

The solution containing the color former may be colorless andtransparent, so that the fingertip hardly shows dirt even in applyingthe solution thereto. Also, the amount of solution to be applied to thefingertip is remarkably reduced, so that almost all the solution on thefingerprint face of the fingertip is transferred to the recording film16.

Accordingly, the solution containing the color former hardly remains atthe fingertip, if a small amount of solution stays, the remainingsolution can be easily removed. In addition, the recording film 16 doesnot need drying after color formation since the coloring reactionbetween the color former and the color developer complete instantly.

FIG. 3A shows enlarged fingerprint images formed according to theembodiment of the present invention in which the microcapsule solutionis used for applying the color former to the fingerprint face of thefingertip; FIG. 3B shows enlarged fingerprint images formed according tothe prior method using the conventional seal ink. In FIGS. 3A and 3B,the left images indicate fingerprint images taken in a normal state thatthe fingertip was pressed correctly, whereas the right images indicatefingerprint images taken in an improperly operated state such that thefingertip was rotated by a degree of about 45° to the counter-clockwisedirection while pressing it against the recording film. Althoughpressurized portions become red in the pressure measuring system"PRESCALE" (trade name), they may be colored with other color such asblack.

As apparent from comparison between FIGS. 3A and 3B, the fingerprintimages formed according to the present invention (FIG. 3A) are clearerthan those formed using seal ink according to the conventional method(FIG. 3B). It should be noted that there is less blurring in the presentinvention even in rotated image. This is because the coloring reactionbetween the color former and the color developer occurs and completesinstantly such that the color former completely reacts to the colordeveloper at the moment when contacting first with the color developer,and unreacted color former does not remain on the fingerprint face ofthe fingertip. For this reason, there will occur no fingerprint imageafter the first coloring reaction even if the fingertip is pressedanywhere else on the recording film 16.

Several types of systems are possible to carry out the presentinvention. For example, as shown in FIG. 4A, a recording sheet 26Aaccording to the present invention can include an electron-donating dyeprecursor applied portion (hereinbelow, referred as to a color-formerapplied portion) 10A which puts a color-former applied film 10 thereon,and a fingerprint image recording portion 16A which puts a recordingfilm 16 thereon, the portions arranged adjacent to each other in placeson the recording sheet 26A. In this embodiment, a fingertip is rubbedagainst the color-former applied portion 10A and then pressed againstthe fingerprint image recording portion 16A, thus generating afingerprint image in such an easy manner.

A recording sheet 26B shown in FIG. 4B is constituted such that thecolor-former applied film 10 is overlaid removably on a fingerprintimage recording portion 16B. It should be noted that a color-formerapplied portion 10B is formed on the upper face of the color-formerapplied film 10 so that the color-former applied portion 10B can beprevented from contacting with the color developer. In this embodiment,the fingertip is rubbed against the upper face of the film 10 and thenpressed against the recording film 16 after tearing the film 10 off. Theremoved film 10 is a disposable item.

Next, a recording sheet 26C shown in FIG. 4C is constituted such that afingerprint image recording portion 16C is formed on the recording sheet26C, but a colorformer applied film 10 shown as a reference numeral 10Cis provided separately from the recording sheet 26C. The recordingsheets shown in FIGS. 4B and 4C each have advantage of making arecording area wide.

Further, the recording portions 16A, 16B and 16C may be each coveredwith a light-shielding film, so that the fingerprint image recorded onthe recording portion 16A, 16B or 16C can be prevented from changing orlosing color, thereby extending a preservation period of the fingerprintimage.

The light-shielding film to be used for the recording sheet in FIG. 4Aor 4C can be overlaid on the upper face of the recording portion 16A or16C. For example, the light-shielding film is bonded to the upper end ofthe recording portion 16A or 16C so that the recording portion 16A or16C can be exposed by rolling up the light-shielding film during takinga fingerprint. Alternatively, the light-shielding film may be providedseparately from the recording sheet 26A, 26C for covering the recordingportion 16A or 16C therewith after taking the fingerprint so that thefingerprint image can be fixed.

In the embodiment shown in FIG. 4B, the support 12 of the color-formerapplied film 10 can be preformed with a light-shielding film. In thiscase, the film 10 remains on the recording sheet 26B to keep therecording portion 16B covered therewith.

In the above embodiments, although the color former is microencapsulatedafter dissolved in oil, the present invention can be applied to a casethat the solution of the color former in the oil is used as it iswithout microencapsulation. In this case, the color former solution maybe soaked up with a sponge or a cloth and, when taking a fingerprint,the fingertip is put into contact with the sponge or the cloth intowhich the solution is soaked so that the solution can be applied to thefingertip. The solution is colorable, but preferably transparent.

Further, the present invention can be applied to a system for takingimages other than the fingerprint image. If articles which are subjectof inspection have uneven surfaces, images of uneven pattern on thesurfaces can be taken easily according to the present invention.

As described above, according to the present invention, a solution of anelectron-donating dye precursor (color former) is applied to afingerprint face of a fingertip and a recording film is pressed with thefingertip so that a fingerprint image can be generated or produced andrecorded. Accordingly, the solution of the electron-donating dyeprecursor which adheres to the fingertip is put into contact with anelectron-accepting color developer so that a coloring reaction occursinstantly, thereby obtaining a clear fingerprint image.

Since the coloring reaction of the electron-donating dye precursor tothe electron-accepting color developer occurs substantially at a moment,an unblurred fingerprint image can be obtained even when performingimproper operation such as to rotate the fingertip while contacting withthe surface applying the electron-accepting color developer thereto.Also, the fingerprint image generated due to the coloring reaction dosenot need drying after taking the fingerprint differently from theconventional system using seal ink, and this makes it possible to makeoffice work efficiently.

On the other hand, a small amount of solution in which theelectron-donating dye precursor is dissolved adheres to the fingertipsuch as not to show a remarkable dirt in general, so that the fingertipdoes not need wiping or can be wiped easily after taking thefingerprint. Therefore, incidental work to the fingerprint takingprocess is not required or remarkably simplified.

If the solution of the electron-donating dye precursor ismicroencapsulated so that the microcapsules containing the solutiontherein can be ruptured merely by pressing them lightly with a finger,the amount of the solution to be applied to the fingertip are easilycontrolled, thereby obtaining desired handling easily.

In the above case, the microcapsules are preferably ruptured underpressure of approximately 0.2 to 0.6 MPa. Also, the amount of thesolution to be applied to the fingertip, the solution containing theelectron-donating dye precursor, is set preferably so that the amount ofthe 5 solution to be transferred from the fingertip to a recording filmfalls in a range of 20 to 100 μg/cm².

A fingerprint image recording sheet practically used to carry out suchmethods includes a fingerprint image recording portion formed byapplying an electron-accepting color developer to a recording paper, andan electron-donating dye precursor applied portion. In such a recordingsheet, if the electron-donating dye precursor is microencapsulated, theamount of the electron-donating dye precursor to be applied to thefingertip is easily controlled and desired handling is obtained.

The fingerprint image recording portion and the electron-donating dyeprecursor applied portion are formed in different regions adjacent toeach other, so that the fingertip is rubbed against one region andpressed against adjacent region, thus making handling remarkably easy.Further, the fingerprint image recording portion can be covered with alight-shielding film capable of opening and closing, so that theelectron-accepting color developer can be prevented from changing orlosing color, and this makes it possible to improve long-rangepreservative property of the recorded fingerprint image.

If the fingerprint image recording portion is covered with a removablefilm and the electron-donating dye precursor applied portion is formedon the upper face of the removable film, a document recording region ofthe recording sheet will be enlarged, thus obtaining a small sizedrecording sheet. In this case, the film is torn off after rubbing theupper face of the film with a fingertip so as to apply theelectron-donating dye precursor to the fingertip. Then, the fingertip ispressed against the fingerprint image recording portion exposed afterremoving the film, thus generating the fingerprint image easily.Alternatively, the film used herein may be a light-shielding film withwhich the fingerprint image recording portion is covered after recordingthe fingerprint on the fingerprint image recording portion, thelight-shielding film does not need preparing separately, and this isconvenient to handle.

What is claimed is:
 1. A fingerprint image recording sheet comprising:afingerprint image recording portion to which an electron-accepting colordeveloper is applied; and an electron-donating dye precursor appliedportion to which a solution of an electron-donating dye precursor isapplied, the electron-accepting color developer being capable ofadsorbing the electron-donating dye precursor to cause a coloringreaction on the fingerprint image recording portion, wherein saidfingerprint image recording portion is covered with a removable film andsaid electron-donating dye precursor applied portion is formed on theupper face of the removable film.
 2. The sheet according to claim 1,wherein the solution of the election-donating dye precursor ismicroencapsulated and applied.
 3. A fingerprint image recording sheetcomprising:a fingerprint image recording portion to which anelectron-accenting color developer is applied; and an electron-donatingdye precursor applied portion to which a solution of anelectron-donating dye precursor is applied, the electron-accepting colordeveloper being capable of adsorbing the electron-donating dye precursorto cause a coloring reaction on the fingerprint image recording portion,wherein said fingerprint image recording portion is covered with alight-shielding film capable of opening and closing and saidelectron-donating dye precursor applied portion is formed on the upperface of the light-shielding film.
 4. The sheet according to claim 3,wherein the solution of the election-donating dye precursor ismicroencapsulated and applied.